Microelectronic features are typically formed in and/or on semiconductor wafers or other microfeature workpieces by selectively removing material from the wafer and depositing insulative, semiconductive and/or conductive materials onto the wafer. Microlithography is widely used in semiconductor processing to pattern small features onto the wafer. A typical microlithography process includes depositing a layer of radiation-sensitive material on the wafer (e.g., photoresist), positioning a patterned mask or mask over the photoresist layer, and then irradiating selected regions of the masked photoresist layer with a selected radiation. The wafer is then exposed to a developer, such as an aqueous base or a solvent, that removes either the irradiated regions or the non-irradiated regions of the photoresist layer. In one case, the photoresist layer is initially generally soluble in the developer, and the portions of the photoresist layer exposed to the radiation through patterned openings in the mask change from being generally soluble to being generally resistant to the developer (e.g., so as to have low solubility). Alternatively, the photoresist layer can be initially generally insoluble in the developer, and the portions of the photoresist layer exposed to the radiation through the openings in the mask become more soluble. In either case, the portions of the photoresist layer that are resistant to the developer remain on the wafer, and the rest of the photoresist layer is removed by the developer to form a pattern of openings in the photoresist layer.
After forming the openings in the photoresist layer, the wafer often undergoes several etching or deposition processes. In an etching process, the etchant removes material by the openings in the photoresist layer, but not material protected beneath the remaining portions of the photoresist layer. Accordingly, the etchant creates a pattern of features (such as grooves, channels, or holes) in the wafer material or in materials deposited on the wafer. These features can be filled with insulative, conductive, or semiconductive materials in subsequent deposition processes to build layers of microelectronic features on the wafer. In other deposition processes, metals or other materials can be plated into the openings of the photoresist layer using electroless or electrolytic techniques. The wafer is subsequently singulated after such processing to form individual chips, which can be incorporated into a wide variety of electronic products, such as computers and other consumer or industrial electronic devices.
Microlithography can be a limiting factor in circuit design because it is challenging to pattern progressively smaller circuit features while still maintaining cost-effective manufacturing. For example, certain sites for contacts in high density contact arrays may have a reduced depth of focus such that they do not have the same contrast level as adjacent contacts. This limits the spacing between the contacts such that there is a minimum pitch for dense contact patterns, which in turn limits the ability to decrease the die sizes and/or the cost of manufacturing semiconductor products.